Hello, welcome to the Flarum community!
I am not aware of any existing functional Xenforo importers at the moment, there is this one for Xenforo 1.5 to Flarum beta 9 https://discuss.flarum.org/d/20882-xenforo-to-flarum-import-migration-scripts, though I do not know if it still does the trick or if it's compatible with your Xenforo instance.
You could hire someone to build a suitable importer however.
